1. Field of the Invention
This invention concerns a coater blade for a coating process, its manufacturing method and its use in a coating process and in the manufacture of many kinds of coated paper, such as coated paper for printing, pressure sensible copy paper, or pressure sensible recording paper, by coating a aqueous emulsion consisting of pigments as the main into the paper.
2. Description of the Prior Art
Up to now, the coater blades used for the coating processes for manufacturing many kinds of coated paper are made up with elastic spring steels (SK-4 or SK-5) or SUS410, which were hardened by quenching and refined in a range of 0.3-0.8 mm in depth, 50-150 mm in width and 1500-7000 mm in length. The coater blades are divided into two types; the bevel type blade, which is used by pressing its pointed end, which has an oblique cut, against the coating paper and the other is the bent-type blade, which is used by pressing the bottom of the pointed end against the coating paper. Though they are used properly depending on the required quantities of coating material, the type of paper used, and the required quality of the product by the users, it seems to be the actual situation that the life-time of the blades has been as short as 4 to 12 hours, or 8 hours on the average, during which the blades wore away or suffered damage, because the blade is scraped continuously with coating paper moving at a high speed, or with an aqueous emulsion.
Therefore, as was shown, in Japan patent Publication No. 1984-88995 as an example, it has been proposed to maintain the stability of the operation in the manufacturing process of the coated paper by decreasing the frequency of exchange of the blade by increasing its life. This has been accomplished by providing a grinding finish after coating by a thermal sprayer with ceramic such as alumina, alumina-titania, or chromium (III) oxide on a part of the surface of the blade. Although this ceramic coated blade made by the thermal spray method could achieve a life of 3-4 times longer after it has been properly used, compared with a usual coater blade made of spring steel, there are some cases that the coater blades are not suitable for use because of coating speckles, depending on the adapted coating materials. The cause may be attributed on one hand to the grinding processing at the contact position of the blade to the coating paper and, on the other hand, to the difficulty in fitting the coater blade to the bending deformation of the backing roll by the better abrasion-resistance of the coating materials. On the other hand, in the case of a conventional coater blade made of non-coated steel, despite its contact position to the coating paper being processed straight by grinding, the reason why it can be used adjustably for every coater is attributed to its short life, in other word, its low resistance to abrasion, which makes the coater blade installed in the coater head wear rapidly to fit along the upper curvature of the backing roll.
As for the other problem, because the coater blade described in Japan Patent Publication No. 1984-88995 is formed in a straight camber, the use of this is almost limited to one in which the backing roll has a slight curvature and, even in this case, it is necessary to install the blade in the coating machine at a high accuracy or there is a tendency to produce a comparatively large amount of loss of the initial coating paper by the occurrence of coating streaks until the blade has adapted to the backing roll. Moreover, in the case of a coating of a non-ceramic material such as hard metals, for example, chromium plating, nickel-phospor alloy plating, and nickel-boron alloy plating, the coater blade has the same tendencies as those of the ceramic-coated blade as long as it is formed in a straight camber.